Traditional gas turbine engine auxiliary power units including an engine core with a combustor which are used to drive a generator typically require a cooling system for the generator. Such a cooling system may include fans and/or ejectors can represent significant power losses and/or create drag penalties in flight.
Moreover, such traditional gas turbine engine auxiliary power units usually have an exhaust with relatively high temperature, requiring the use of high temperature materials in the exhaust duct walls, which may represent a significant cost.